1. Field of the Invention
The present invention relates to an electronic timepiece having a date wheel for advancing control of the electronic timepiece, and particularly to an electronic timepiece using both a mechanical system for detecting a mechanical position of a 24 hour wheel and an electronic system for counting an indicator of the timepiece for detecting date switching time.
2. Description of the Prior Art
In an electronic timepiece of so-to-speak analog display, it is currently general to mount a calendar mechanism which is recognized by a user as a naturally provided function. Generally, there is known a calendar mechanism having a display mode in which a window is provided at the 3 o""clock position on a dial and numerals are viewed from inside of the window or a display mode in which month and date are indicated by an indicator as in time display.
In either of the above-described display modes, the display state indicating month or date is changed in accordance with change of actual date or month and accordingly, the date switching time needs to be detected. The change of the display state is realized by feed control of a date wheel operating through movement of a numeral disk or an indicator. In order to detect the date switching time, generally, there is adopted a mechanical system or an electronic system.
According to the mechanical system, an electrode is attached orthogonally to a shaft of a 24 hour wheel constituting one of the front train wheels and the electrode is brought into contact with a specific electrode pattern on a circuit board functioning also as a bearing of the 24 hour wheel to thereby detect the date switching time. For example, the above-described electrode is formed in a strip-like shape the center of which is disposed at the shaft of the 24 hour wheel and both ends of the electrode conduct electricity between two electrode patterns which are separated from each other on the same circular rim of the circuit board to thereby detect the date switching time.
Meanwhile, according to the electronic system, pulses for controlling the indicators of the timepiece are electronically counted with the date switching time as a reference and it is monitored whether a counted result reaches a predetermined number of pulses in correspondence with elapse of 24 hours and the reached time point is detected as the date switching time.
However, according to the conventional electronic timepiece, in detecting the date switching time by the mechanical system, generally, voltage (Vdd) of a logical level xe2x80x9cHxe2x80x9d is applied to one of the above-described two electrode patterns and it is necessary to monitor whether CPU makes the change to the logical level state of voltage of the other electrode pattern (hereinafter, referred to as detecting terminal), that is, the logical level xe2x80x9cHxe2x80x9d.
In this case, a signal inputted to the CPU via the detecting terminal needs to stably maintain the logical level without undergoing influence of noise. Hence, normally, there is constructed a constitution in which a pull-down resistor is connected to the detecting terminal and a signal at xe2x80x9cLxe2x80x9d level is always inputted to the side of CPU in a state other than detecting the date switching time. Therefore, there is brought about a state in which power is always dissipated via the pull-down resistor although the dissipated power is very small and the dissipation of power influences on the life of a battery for a wrist watch or the like driven by a small-sized battery.
Meanwhile, according to the conventional electronic timepiece, in detecting the date switching time by the electronic system, when a battery is interchanged, in order to set a reference of counting pulses, it is necessary to inform the indicator position giving current time to CPU, which is difficult to realize for the electronic timepiece having operating means of only a winding stem for correcting time.
The invention has been carried out in view of the above-described and it is an object thereof to provide an electronic timepiece which is capable of resolving the problem of power dissipation in the mechanical system by also using an electronic system in addition to the mechanical system and which is capable of accurately detecting date switching time with no need of special operation after changing the battery or correcting time using the winding stem.
In order to achieve the above-described object, according to an aspect of the invention, there is provided an electronic timepiece which is an electronic timepiece having a calendar function by a feed control of a date wheel, the electronic timepiece comprising a 24 hour wheel rotating by once per day based on movement of an indicator such as an hour hand by way of a train wheel, a contact spring fixed to the 24 hour wheel to rotate in connection with the 24 hour wheel and having conductivity (corresponding to a contact spring 43, mentioned later), a circuit board formed with a first electrode pattern (corresponding to a detecting terminal 41, mentioned later, hereinafter, referred to as detecting terminal) and a second electrode pattern (corresponding to an electrode 42, mentioned later, hereinafter, referred to as electrode) electrically connected to each other by the contact spring only at a specific rotational position (date switching position) of the contact spring, a switching circuit (corresponding to a pull-down resistor 52 and an NMOS transistor 53, mentioned later) to pull up or pull down a voltage level of the detecting terminal to a first voltage level (power source potential Vdd or ground potential) in a case of an ON state, and controller (corresponding to CPU 10, mentioned later) to bring the switching circuit into the ON state only for a predetermined period of time and advancing the date wheel when the voltage level of the detecting terminal reaches a second voltage level (voltage different from first voltage level and ground potential or power source potential Vdd) supplied to the electrode in the predetermined period of time.
According to an aspect of the invention, in detecting the rotational position of the contact spring above the 24 hour wheel, the controller brings the detecting terminal into a state of being supplied with the ground potential or the power source potential Vdd via the pull-down resistor or the pull-up resistor by the switching circuit only for a necessary predetermined time period and accordingly, for example, when reliability of detection of the date switching time is to be improved when using the above-described electronic system also, detection of the date switching time by the mechanical system can be actuated only when necessary.
Further, according to another aspect of the invention, there is provided the electronic timepiece further comprising a detector (corresponding to the operation of a winding stem, mentioned later) for detecting termination of the operation of interchanging a battery or correcting the time and outputting an initializing signal, wherein the controller brings the switching circuit into the ON state when the initializing signal is inputted, brings the switching circuit into an OFF state when a specific rotational position of the contact spring is detected, starts a counting operation at intervals of 24 hours by a predetermined clock pulse and advances the date wheel at every time at which the result of the counting operation reaches a value indicating elapse of 24 hours.
According to an aspect of the invention, detection of the date switching time by the mechanical system is carried out only in the initialized state after changing a battery or correcting time which is detected by the detector and thereafter, by the controller, the operation of pulling up or pulling down causing dissipation of power in the mechanical system is removed by bringing the switching circuit into the OFF state and the operation can proceed to detection of the date switching time by the electronic system.
Further, according to another aspect of the invention, there is provided an electronic timepiece wherein the controller starts a counting operation different from the counting operation of 24 hours by the predetermined clock pulse when the switching circuit is brought into the OFF state and executes a processing the same as a processing in a case in which the initializing signal is inputted to the controller also when the result of the counting operation reaches a predetermined value.
According to an aspect of the invention, also in the case of operation other than the operation by the user such as interchanging a battery or correcting time, in the electronic timepiece which is brought into a state of detecting the date switching time by the electronic system, when the predetermined time period is counted by the controller, detection of the date switching time by the mechanical system can automatically be carried out.
According to another aspect of the invention, there is provided the electronic timepiece, further comprising detector for detecting termination of an operation of interchanging a battery or correcting time and outputting an initializing signal, wherein the controller brings the switching circuit into an ON state when the initializing signal is inputted, starts a counting operation of 24 hours by a predetermined clock pulse when a specific rotational position of the contact spring is detected, successively stores the result of the counting operation correcting the previous value every time the specific rotational position of the contact spring is detected, brings the switching circuit into an OFF state when the result of the counting operation stored reaches a predetermined number of times (for example, 3 times), corrects the determination standard of the counting operation of 24 hours by using the stored correction value, starts again the counting operation at intervals of 24 hours and thereafter advances the date wheel at every time at which the result of the counting operation reaches the determination standard.
According to an aspect of the invention, in the initialized state after interchanging a battery or correcting time which is detected by the detector, detection of the date switching time by the mechanical system is carried out only for a certain fixed time period (constant number of times), counting by the electronic system is simultaneously carried out and the result of counting in the time period of executing the mechanical system can be collected. Accordingly, thereafter, the determination standard value for counting 24 hours can be adjusted based on the collected result of the counting and when the mechanical system is shifted to the electronic system, the date switching time can be detected more accurately.